Export JIRA Data
Generally, there are two main approaches to backup your JIRA data. The first one is to back up your database in which JIRA info is stored. The second one is to use the “Backup Data to XML feature”, which is a JIRA feature. Personally, I prefer the second one, because it can be restored to any database engine (MySQL, MSSQL, etc). In addition, as far as it is Xml, it can be compressed to a great extent.
I have written a little ruby utility that uses JIRA's REST API to export all tickets for a given project to the local file system. It is available as a ruby gem, so the installation is trivial.
The tickets are saved as individual JSON files. The tool also supports incremental updates.